[GitHub] [xerces-c] rouault commented on a diff in pull re quest #51: [XERCESC-2241] Fix integer overflows in DFACon tentModel class

rouault commented on code in PR #51:
URL: https://github.com/apache/xerces-c/pull/51#discussion_r986039665


##########
src/xercesc/validators/common/DFAContentModel.cpp:
##########
@@ -661,8 +662,15 @@ void DFAContentModel::buildDFA(ContentSpecNode* const curNode)
     //  in the fLeafCount member.
     //
     fLeafCount=countLeafNodes(curNode);
+    // Avoid integer overflow in below fLeafCount++ increment
+    if (fLeafCount > std::numeric_limits<unsigned int>::max() - 1)

Review Comment:
   fLeafCount is actually declared as unsigned int at line 236 of DFAContentModel.hpp (which is already much bigger than what is reasonable in practice :-))



##########
src/xercesc/validators/common/DFAContentModel.cpp:
##########
@@ -661,8 +662,15 @@ void DFAContentModel::buildDFA(ContentSpecNode* const curNode)
     //  in the fLeafCount member.
     //
     fLeafCount=countLeafNodes(curNode);
+    // Avoid integer overflow in below fLeafCount++ increment
+    if (fLeafCount > std::numeric_limits<unsigned int>::max() - 1)
+        throw OutOfMemoryException();
     fEOCPos = fLeafCount++;
 
+    // Avoid integer overflow in below memory allocatoin
+    if (fLeafCount > std::numeric_limits<size_t>::max() / sizeof(CMLeaf*))

Review Comment:
   > Would it be possible to add brackets around the division for clarity?
   
   this is the best way I can think of that doesn't rely on doing overflow arithmetic... As it is unsigned type, we could do overflow arithmetic as it is well defined in C/C++, but I tend to fuzz software with -fsanitize=unsigned-integer-overflow because in practice > 90% unsigned overflows that occur are actually bugs



##########
src/xercesc/validators/common/DFAContentModel.cpp:
##########
@@ -661,8 +662,15 @@ void DFAContentModel::buildDFA(ContentSpecNode* const curNode)
     //  in the fLeafCount member.
     //
     fLeafCount=countLeafNodes(curNode);
+    // Avoid integer overflow in below fLeafCount++ increment
+    if (fLeafCount > std::numeric_limits<unsigned int>::max() - 1)
+        throw OutOfMemoryException();
     fEOCPos = fLeafCount++;
 
+    // Avoid integer overflow in below memory allocatoin

Review Comment:
   fixed



##########
src/xercesc/validators/common/DFAContentModel.cpp:
##########
@@ -1364,14 +1372,27 @@ unsigned int DFAContentModel::countLeafNodes(ContentSpecNode* const curNode)
         if(nLoopCount!=0)
         {
             count += countLeafNodes(cursor);
-            for(unsigned int i=0;i<nLoopCount;i++)
-                count += countLeafNodes(rightNode);
+            const unsigned int countRight = countLeafNodes(rightNode);
+            // Avoid integer overflow in below multiplication
+            if (countRight > std::numeric_limits<unsigned int>::max() / nLoopCount)

Review Comment:
   cf above comments regarding data type
   
   brackets added



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